The present invention relates to surface cleaning apparatus, and particularly to such apparatus employing air assist or air blast pickup heads.
Air assist pickup heads deliver air under pressure to an exhaust chamber. The air under pressure sweeping over the surface being cleaned tends to loosen debris which is then exhausted through an exhaust line joined to the exhaust chamber. A sweeper having a pickup head of this type is disclosed in U.S. Pat. No. 3,512,206, issued to Mr. B. W. Young on May 19, 1970. The exhaust chamber is enclosed on all sides so that it is somewhat sealed with respect to the atmosphere. The front wall of the exhaust chamber is sealed by means of a flexible flap which allows debris and the like to pass thereunder and into the exhaust chamber.
This type of pickup head is quite effective as a result of the employment of a blast of air to loosen dirt on the surface to be cleaned. In order to keep dust and the like to a minimum, it is fairly important that the exhaust chamber be relatively well sealed with respect to the atmosphere. Thus, dust and debris kicked up by the air blast are exhausted from the exhaust chamber without escaping to any great extent to the air. Typically, some air is drawn in from the atmosphere from the side walls and front flap of the exhaust chamber as a result of the fact that a small bleed-off is inherent in the flow circuit. Some of the air which is drawn out of the exhaust chamber by the blower is exhausted to the atmosphere, as a result of a small amount of unavoidable leakage, rather than being returned to the air delivery plenum chamber with the bulk of the air. Typically, such bleed-off amounts to about 1% of the air being circulated and is probably never more than 5 to 10%. In some systems, a bleed-off port is purposely provided for bleeding off these small amounts of air.
One drawback to such a system is that the pickup head does not readily ingest larger articles of debris and the like. The front flap of exhaust chamber is flexible so that theoretically large items of debris and litter can be drawn thereunder. As a practical matter, however, such ingestion poses a mettlesome and heretofore unsolved problem.